If you have projects residing in multiple folders, try and navigate to another folder by using the "back arrow" icon in the upper left. Once you're out of the folder you just left and try to choose another, PS Touch simply does not respond. (It doesn't lock up; it just doesn't register tapping another folder.) I could have sworn I was able to export images in multiple folder at once before.

Using a Google Nexus 2013 Wi-Fi model with Android Lollipop 5.0.1. I can record a movie if need be illustrating this potential issue.